Conventionally, electric machines have their power electronics outside the housing of the electric machine. There are at least two reasons for separating the power electronics from the electric machine. First, the volume taken up by the power electronics is such that it is difficult to package the electric machine in the intended application. Second, the environment inside an electric machine housing is significantly harsher than the conventional environment for power electronics.
One significant problem that must be addressed in power electronics apparatus is heat generation. Conventionally, a heat spreader is coupled to the power electronics to enhance heat dissipation. Metals (such as copper) are good for heat spreading, as they quickly conduct the heat away from the power die. Ceramics are not as good since their thermal conductivity is not nearly as good. Thus, metals are able to carry heat away from the die much more effectively than a ceramic substrate.
Power dies, which are central to power electronics, create a great deal of heat and must have some form of cooling technology in place to dissipate heat. Power dies are typically packaged in a large insulating (typically ceramic) substrate. One of the reasons the ceramic substrate is used is to prevent stressing the die. More specifically, the coefficient of thermal expansion (CTE) of the ceramic substrate is more closely matched to the power die than to a metal substrate. This insulating or ceramic substrate is typically soldered to a metal heat spreader. The metal heat spreader is then mounted to a heatsink in the power electronics. The ceramic packaging, metal baseplate, heatsink and solder add to thermal resistance. A system that has a very low thermal resistance will be able to cool more efficiently.
The cost and size of an electric machine can be reduced if the power electronics can be made so compact to be housed within the electric machine. Unfortunately, conventional inverters and the required cooling apparatus are too bulky to be placed inside an electric machine. Thus, a new and improved method and system for packaging power electronics is needed.